1. Field of the Invention
The present invention relates to a stator of an electric rotating machine, the stator including a stator core constituted of a plurality of split cores fitted to an outer casing by shrink-fitting, for example.
2. Description of Related Art
In recent years, there is a growing need for a compact and high-output electric rotating machine usable as an electric motor or an alternator. One of the reasons is that the space for accommodating an electric rotating machine mounted on a vehicle is becoming smaller and smaller, while the output required of the electric rotating machine is becoming higher and higher.
It is known to dispose a plurality of split cores in a ring assembly, and fit the ring assembly of the split cores to a cylindrical casing (outer casing) at its outer circumference to form a stator core. For example, refer to Japanese Patent Application Laid-open No. 2002-51485.
This patent document discloses using a shrink-fitting method to fit the ring assembly of the split cores to the outer casing. In this method, the outer casing whose inner diameter is slightly smaller than the outer diameter of the ring assembly of the split cores is set in place, and the ring assembly is fitted into the outer casing which is being heated so that its inner diameter expands. After completion of the shrink-fitting, the ring assembly of the split cores and the outer casing are fixed firmly to each other by the stress due to difference between their diameters.
Meanwhile, the thickness of the outer casing is required to be as thin as possible in order to provide a compact and high output electric rotating machine. However, reducing the thickness of the outer casing causes a problem that the roundness of the above ring assembly of the split cores is lowered because of reduction of rigidity of the outer casing.